That's just wishful thinking. Who sells 'quality guarantees'? It's always packaged as 'support', which boils down to support personnel man hours. So still pay for worked hours.

If you fix bugs you need to contribute back to the trunk, at which point anybody can use them without paying for the dev time. Paying devs to work on such a project is useful mostly as a marketing tactic, and to develop in-house expertise on the tech.

Let's face it, all open source business models boil down to repackaged and rephrased consultancy work, which scales by making more paid hours. It's as simple as that.